Polymer materials have been of great interest in the research and development of integrated circuits (IC) and micro-electro-mechanical systems (MEMS) recently due to their relatively low cost and much simpler processing techniques. Hot embossing of polymers is a promising alternative to the traditional silicon processes. It fulfills the demand for low-cost methods of mass production of micro-components and micro-systems. Also, the polymer materials for hot embossing are much cheaper than silicon wafers. Moreover, for hot embossing of polymer materials, complex micro-machining steps are only necessary to fabricate a master mold. Once the master mold is complete, the desired micro-structures can be easily batch replicated by a hot embossing process.
Hot embossing is essentially the stamping of patterns into a polymer by raising the temperature above the polymer's glass transition point. During the last several years, hot embossing technology has been developed and applied in both laboratories and industry in a variety of fields. For example, hot embossing lithography (HEL) has been proposed as one of the most promising methods to replace e-beam or x-ray lithography as feature sizes are scaled down to nanometers for large area substrates (such as Si wafers of four inches or greater) and mass production. In HEL, a master mold is made by e-beam lithography and appropriate etching processes and then nano-patterns are batch imprinted on the large-scale substrates by hot embossing[1]–[3]. Hot embossing has been successfully applied to the fabrication of micro-fluidics devices on PMMA substrates for analytical chemistry and biomedical applications such as micro-total-analysis-systems (u-TAS), i.e., the lab-on-a-chip[4][5]. As mentioned previously, polymer micro-fabrication by hot embossing is also becoming increasingly important as the low-cost alternative to silicon or glass-based MEMS technologies[6]–[10].
An area of electronics which has promising potential application with polymer based circuits is tunneling sensors. Since the Nobel Prize was awarded to Binnig and Rohrer in 1986 for building the first scanning tunneling micro-scope (STM) by utilizing tunneling current, the possibility of producing a high-sensitivity tunneling displacement transducer has been actively explored. Several years after the advent of the first tunneling transducer[11], the sensors with displacement resolution approaching 10−4 Å/√Hz were developed by Waltman[12] and Kenny[13]. In electron tunneling transducers, a 1% change in 1.5 nA current between tunneling electrodes corresponds to displacement fluctuation of less than 0.1 Å. This high sensitivity is independent of the lateral size of the electrodes because the tunneling current occurs between two metal atoms located at opposite electrode surfaces. Due to its high sensitivity and miniature size, micro-machined tunneling transducers make it possible to fabricate a high performance, small size, light mass, inexpensive accelerometer, which is in great demand in applications such as micro-gravity measurements, acoustic measurements, seismology, and navigation.
An electrostatic comb drive is one of the most important components in MEMS. A standard comb drive is formed by two sets of fingers with uniform gaps. One set is fixed on the substrate, which is called a fixed, or stationary finger. The other set is separate from the substrate and is called a moving finger. Moving fingers can move either laterally with the gaps fixed or vertically with the gaps closing to one side or the other. Normally the laterally moving comb drive works as an electrostatic actuator. In this way, it can give a constant force and has a large stroke distance. Gap-closing combs often work as a capacitive sensor. In this way, the capacitance variation is approximately inversely proportional to the square of gap distance. Much research and development on varieties of comb drives have been published since it was first presented by Tang, et al[14][15]. William A. Johnson and Larry K. Warn gave a thorough analysis on the physics of comb drives in their paper, “Electrophysics of Micro-mechanical Comb Actuators”[16]. W. Ye, et al presented an “optimal shape design of two and three dimensional comb drives”, in which the quadratic or cubic force profiles, beside the linear one, under constant bias voltage by changing finger shape were given[17][18]. M. Steven Rodgers, et al presented an actuation system with large force, low-voltage, and efficient area[19]. Other investigations on the comb drive include an asymmetric comb drive in out-of-plane and torsional motions[20], a comb drive with extended travel[21], a sub-micron gap comb drive micro-actuators[22], and an angular comb drive actuator[23] have also been published.
However, despite the advances in polymer circuits and tunneling sensors, there is still a need for more efficient methods of manufacturing polymer circuits and it would be particularly useful to develop a polymer based tunneling sensor device. Therefore, it is an object of the present invention to provide a novel polymer based tunneling sensor which fulfills these needs. It is also an object of this invention to provide a novel reduced noise tunneling sensor.